gh-145633: deprecate float.__getformat__() class method

[skirpichev]

• Issue: Remove "unknown_format" code path in PyFloat_Pack/Unpack*() #145633

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📚 Documentation preview 📚: https://cpython-previews--146400.org.readthedocs.build/

[skirpichev]

CC @serhiy-storchaka

[vstinner]

LGTM

[skirpichev]

@vstinner, please don't merge. I would appreciate a second review.

[serhiy-storchaka]

in general, I like removing private, unsystematic, undocumented methods which only serve internal debugging purpose. There some things in bytearray and set. But first we need to look at their history and ask authors who added them. Do they still need them? I think that special testing module would be better place for such things.

[skirpichev]

But first we need to look at their history and ask authors who added them. Do they still need them?

The __getformat__() class method, together with removed __setformat__() was added by ba283e2. CC @mwhudson

I think that special testing module would be better place for such things.

This private API now is helpful only for alternative implementations, which run the CPython test suite. I don't see how a special testing module would help here.

See #145633 (comment) for some usage examples.